4 Valve Description
22 of 72
0570.81/22-EN
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The blow-off pressure is set via the threaded insert.
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Stellited seat
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Lead-sealed screw prevents unauthorised manipulation of set blow-off pressure.
Variants
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Bursting disc (UGSV and UGSVA)
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Blocking device
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With lockable shut-off valve
4.5.1.3 Heating up of trapped liquids
The problem of trapped liquids heating up primarily concerns gate valves.
If liquid remains in the body after pressure testing, for instance, or if condensate
develops due to certain operating conditions, there is a risk of an impermissible
pressure increase if the body is heated up by hot water or steam in one or both the
connected pipes. The potential pressure increase depends both on the temperature
and the extent to which the body is filled with liquid and may reach impermissible
values very quickly.
The problem of trapped liquids heating up inside the valve is particularly dangerous
on gate valves with a pressure seal bonnet as the bonnet seal becomes tighter with
rising pressure. The pressure may reach several times the operating pressure.
On gate valves with a bolted bonnet, an impermissible increase in pressure will cause
leaks at the bonnet gasket. This effect needs to be taken into account and prevented
by the purchaser by taking suitable measures as required, e.g. by fitting a body
pressure relief valve and providing for controlled drainage.
For gate valves with a pressure seal bonnet, by contrast, a body pressure relief valve
is mandatory if excessive heating of trapped liquids is potentially a problem. The
body pressure relief valve ensures that the body is protected against excessive loads
and deformation under all operating conditions, thus avoiding incidents which may
compromise safety.
The likelihood of trapped liquid heating up varies depending on the system and must
be individually assessed for each gate valve by the purchaser. It is therefore necessary
to order the body pressure relief valve and the gate valve separately.
4.5.1.4 Function
Body pressure relief valves are available in the following designs:
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Spring-loaded body pressure relief valve (UGS)
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Spring-loaded body pressure relief valve with bursting disc (UGSV)
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Non-spring-loaded designs with bursting disc in combination with a lockable
globe valve (UGSVA).
Spring-loaded body
pressure relief valve (UGS)
Stainless steel valve disc 350 is pressed onto the stellited seat of pipe union 731 by
means of adjustable spring assembly 950 via disc 550.1 and rod 574, ensuring tight
closure.
The required pre-loading of disc springs 950 is adjusted via screw-type body 734,
supported by needle bearing 32-2. Screw-type body 734 is locked in position by
means of screw 900.
The blow-off pressure is set at the factory and stamped on the body pressure relief
valve. It is determined by the respective valve type, the operating data and the max.
permissible body load.
Every body pressure relief valve is tested and lead-sealed. Removal of the lead seal
will void all warranty claims.
Setting and testing are performed on the basis of work instructions or parts list
specifications using special testing equipment. Re-setting can only be performed at
the supplying factory.
